Method for preparing a resist pattern of t-shaped cross section

ABSTRACT

A resist pattern formed on a substrate has a T-shaped cross section including a stem portion extending from the substrate surface and a cap portion connected to the stem portion and spaced from the substrate surface. Provided that α is a minimum of the angle which is defined between a tangent at the lower edge of the cap portion and the substrate surface, and h is the spacing between the lower edge of the cap portion and the substrate surface at an intermediate position, α and, h fall within a range defined and encompassed by tetragon ABCD wherein A: α=0°, h=0.01 μm, B: α=20°, h=0.01 μm, C: α=20°, h=0.2 μm, and D: α=0°, h=0.3 μm. In a patterning process including the steps of coating of a resist composition to form a resist coating, exposure, reversal baking and development, at least one condition is changed by reducing the thickness of the resist coating, reducing an exposure dose, lowering a reversal baking temperature, reducing a reversal baking time, increasing a developer temperature or extending a developing time such that a resist pattern of T-shaped cross section may be formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a resist pattern of T-shaped cross section,its preparation, and a magnetoresistance thin film element comprising amagnetoresistance film, an electrode film therefor, and a shield film atleast one of which is formed using the resist pattern.

2. Prior Art

Several methods are known in the art for forming resist patterns ofinverted trapezoidal or T-shaped cross section.

(A) Resist patterns of inverted trapezoidal cross section are formedusing single layer resists. In one process (a), a single layer ofnegative resist is used. For example, a resist pattern is formed byexposing a negative resist coating to UV radiation by a conventionaltechnique except that the dose of exposure is reduced, followed bypatterning as disclosed in Japanese Patent Application (JP-A) No.136226/1986.

In another process (b), a single layer of positive resist is used. Thereare known several variants which are described below. (i) The substrateside of a resist is set at a lower temperature than the surface sideduring prebaking and postbaking steps. The temperature control duringprebaking is described in JP-A 72678/1979 and the temperature controlduring postbaking is described in JP-A 101218/1991. (ii) A positiveresist film for electron beams is exposed to deep-UV radiation asdisclosed in JP-A 50423/1989. (iii) A novolak resist is coated andmaintained in high vacuum prior to exposure as disclosed in JP-A257817/1991. (iv) A resist coating on a transparent substrate is exposedto UV radiation from both the front and rear surfaces as disclosed inJP-A 37275/1993. (v) When a positive resist is exposed to electronbeams, the exposure time is reduced by once forming a pattern portionand a non-pattern portion, forming a protective film thereon, andremoving the non-pattern portion utilizing the protective film asdisclosed in JP-A 147261/1976. (vi) A resist polymer having a desiredcoefficient of UV absorption is used or a resist having a controlledamount of crosslinking agent added is used as disclosed in JP-A16527/1983. (vii) A photoresist colored with a dye capable of absorbingexposure light is coated onto a substrate and the coating is dipped in asolvent to control the distribution of coloring density in the resist ina thickness direction as disclosed in JP-A 284851/1989.

In a further process (c), a single layer of positive resist having animage reversal function is used. Typically resists commerciallyavailable from Hoechst under the trade name of Resist AZ5200E series areused. A method for forming a resist pattern of inverted trapezoidalcross section using these resists is known. Reference is made to thebrochure of Resist AZ5200E series, M. Bolzen, "Submicron processingtechnology by image reversal of positive photoresists," Densi-Zairyo(Electronic Material), 6, 1 (1986), and M. Spac et al., "Mechanism andlithographic evaluation of image reversal in AZ5214 photoresist," Proc.of conference on photopolymers principle processing and materials,Ellenville (1985). These resist materials are obtained by addingnegative working agents such as basic amines to positive resistcompounds comprising a mixture of alkali soluble phenol resin andnaphthoquinonediazide for imparting an image reversal function.

(B) Resist patterns of T-shaped cross section are also known. One methoduses a single layer of resist. A negative resist is exposed using twotypes of charged beams having different ranges in the resist asdisclosed in JP-A 105423/1987. It is seen from the patent publicationthat a pattern of T-shaped cross section changes into a pattern ofrectangular cross section as a result of shrinkage after rinsing anddrying. Another method uses dual layers of positive resist. (i) Doubleexposure is carried out in appropriate doses. First exposure in apredetermined dose corresponds to a predetermined pattern shape andsecond exposure in a predetermined dose corresponds to a center portionof the same pattern shape (see JP-A 141548/1987). (ii) Upper and lowerlayers of electron beam resist separated by an intervening layer aresimultaneously exposed to a predetermined pattern (see JP-B 55208/1988).(iii) On the surface of a first photoresist film is formed a modifiedlayer which is resistant to development of a second photoresist film(see JP-A 65139/1990). (iv) A resist film of two layer structure isprovided wherein a pattern opening in the lower layer of resist at itsupper surface is wider than a pattern opening in the upper layer ofresist at its lower surface (see JP-A 208934/1990).

Among the above-described prior art techniques, most techniques formresist patterns of inverted trapezoidal cross section. Some techniquescan form resist patterns of T-shaped cross section, but are verydifficult to carry out in practice since two layers of resist must beused or exposure must be done twice.

Methods for forming electrode patterns on substrates include a lift-offmethod, a milling patterning method, and a combined one. These methodsare briefly described as well as the reason why resist patterns ofT-shaped cross section are desirable.

Milling Patterning

A method for forming a pattern by ion milling is shown in FIG. 2. Themethod involves the steps of forming a film to be milled over the entiresurface of a substrate, forming a resist layer thereon, patterning theresist layer into a resist cover, and ion milling the film through theresist cover as a mask. Thereafter, the resist cover is removed bydissolving in organic solvent or reducing to ashes, obtaining a milledor patterned film.

In the case of a resist cover of rectangular or inverted trapezoidalcross section as in prior art examples, there is a possibility that whena film to be milled is etched by the ion milling technique, particleswhich are etched out of the film scatter and deposit on the side wall ofthe resist cover again and the deposit grow from the side wall so as tobe continuous to the surface of the film being milled as seen from FIG.3. When the resist cover is removed, the re-deposited layer can be leftas minute protrusions on the surface of the milled film.

In the case of a resist cover of T-shaped cross section, althoughparticles which are etched out of the film scatter and deposit on theresist cover again, the deposit layer will not grow to be continuous tothe surface of the film being milled insofar as the neck portion at thebottom of the resist cover is high enough as seen from FIG. 4. Then whenthe resist cover is removed, the re-deposited layer is removedtherewith. A milled or patterned film of quality is obtained since there-deposited layer is never left on the surface of the milled film

Lift-off

The lift-off process is described by referring to the formation ofanother patterned film on the above-mentioned milled and patterned film.This lift-off process is used when a lead layer is formed on amagnetoresistance film, for example.

One exemplary lift-off process is described with reference to FIG. 5. Asubstrate having a film to be milled is furnished. Step (1) is to millor pattern the film on the substrate. Step (2) is to apply a resistlayer on the milled or pattern film and pattern it into a resist cover.In step (3), a film of metal or ceramics to be patterned is formed overthe entire surface of the substrate including the patterned resistcover. In step (4), the structure is dipped in an organic solventcapable of dissolving away the resist cover, thereby removing thoseportions of the film overlying the resist cover while those portions ofthe film in direct contact with the substrate are left. A patterned filmis formed in this way.

This process requires that the organic solvent fully penetrate throughthe resist. When the resist pattern has an inverted trapezoidal crosssection as in prior art examples, however, the film as deposited cancontact the resist pattern side wall too to cover the resist pattern asshown in FIG. 6. This extra coverage prevents the organic solvent fromfully penetrating through the resist pattern, failing to remove theresist pattern.

In contrast, in the case of a resist pattern having a T-shaped crosssection wherein the height of a neck portion at the bottom of the resistpattern is less than the thickness of a film deposited over the entiresurface of a substrate, as shown in FIG. 7, while a film is deposited onthe top and side wall of eaves of a resist pattern during deposition, nofilm is deposited near the neck portion which is shaded by the eaves ofthe resist pattern. Consequently, the deposited film does not completelycover the resist pattern. Since the organic solvent can penetrate intothe resist pattern through the neck portion, that portion of thedeposited film overlying the resist pattern can be removed together withthe resist pattern.

Combined Milling Patterning/Lift-off

One exemplary combined milling patterning/lift-off process is describedwith reference to FIG. 8. In step (2), a film to be milled is formedover the entire surface of a substrate. In step (3), a resist layer isformed thereon and patterned into a resist cover. The resist cover is ofinverted trapezoidal cross section in the illustrated example. Then thefilm on the substrate is patterned through the resist cover by ionmilling at step (4). The resist cover which has been used for themilling purpose is not removed, but utilized further as a resist coverfor a subsequent lift-off step. In step (5), metal or ceramic materialis deposited on the entire surface of the substrate. By dissolving awaythe resist cover with an organic solvent, that portion of the depositedfilm on the resist cover is removed together with the resist cover. Asshown in step (6), a continuous film consisting of the milled filmportion and the deposited film portion left after the lift-off step isobtained on the substrate surface.

In the case of a resist cover of rectangular or inverted trapezoidalcross section as in prior art examples, there is a possibility that thefinally obtained continuous film contains minute protrusions left at theboundary between the milled film portion and the deposited film portionleft after the lift-off step for the above-described reason. Sometimes,the resist cover cannot be removed.

In the case of a resist cover of T-shaped cross section, these problemsdo not occur for the above-described reason. A satisfactory continuousfilm consisting of the milled film portion and the deposited filmportion left after the lift-off step is obtained on the substratesurface.

The prior art is successful in producing a resist pattern of invertedtrapezoidal cross section from a single layer of resist, butunsuccessful in producing a resist pattern of T-shaped cross section atan acceptable contrast. FIGS. 17 to 20 show prior art resist patterns ofinverted trapezoidal cross section produced from a single layer ofresist, which are duplicates from the brochure of AZ5200E. The radiationused for patterning is excimer laser light in FIG. 17, i-line in FIG.18, g-line in FIG. 19, and broad band light inclusive of i, g andh-lines in FIG. 20. Any type of radiation fails to form a pattern ofT-shaped cross section.

If one attempts to form a resist pattern of T-shaped cross section inaccordance with a prior art technique using two layers of resist, theprocess is not only laborious, but fails to produce a resist pattern ofT-shaped cross section at an acceptable contrast because intermixingbetween the resist layers occurs at their interface.

As a consequence, a resist pattern of T-shaped cross section with anacceptable contrast is never available in the prior art. If an electrodepattern for a magnetoresistance film of a magnetoresistance thin filmelement is formed using a prior art resist pattern of indefiniteT-shaped cross section, the probability that the electrode material willbe left at areas other than the necessary electrode pattern is high,resulting in a high percentage of rejection.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a resistpattern of T-shaped cross section with an acceptable contrast which isuseful in the manufacture of an electrode pattern for amagnetoresistance thin film element with the advantage of asignificantly reduced percentage of rejected parts.

Another object is to provide a magnetoresistance thin film elementcomprising an electrode pattern or the like formed using the resistpattern.

In a first aspect, the preset invention provides a substantiallyhomogeneous resist pattern which is formed on a surface of a substratefrom a resist composition comprising a positive resist compoundcontaining a mixture of an alkali soluble phenol resin and anaphthoquinonediazide and a negative working agent added to the positiveresist compound for imparting an image reversal function. The resistpattern has a T-shaped cross section including a stem portion extendingfrom the substrate surface and substantially constituting the verticalbar of T and a cap portion connected to the stem portion, opposed to thesubstrate surface with a spacing and substantially constituting thehorizontal bar of T. Provided that α is a minimum of the angle which isdefined between a tangent at the lower edge of said cap portion opposedto the substrate surface and the substrate surface, and h is the spacingbetween the lower edge of the cap portion and the substrate surface atan intermediate position between the crossing Wo between a lineextending from the outermost edge of the cap portion perpendicular tothe substrate surface and the substrate surface and the crossing Wibetween the side edge of the stem portion and the substrate surface, theminimum angle α and the spacing h fall within a range defined andencompassed by tetragon ABCD in a h-α graph wherein

A: α=0°, h=0.01 μm,

B: α=20°, h=0.01 μm,

C: α=20°, h=0.2 μm, and

D: α=0°, h=0.3 μm.

In one preferred embodiment, α and h fall within a range defined andencompassed by tetragon AXYZ in the h-α graph wherein A: α=0°, h=0.01μm, X: α=5°, h=0.01 μm, Y: α=5°, h=0.15 μm, and Z: α=0°, h=0.15 μm. In afurther preferred embodiment, α and h fall within a range defined andencompassed by tetragon AXGH in the h-α graph wherein A: α=0°, h=0.01μm, X: α=5°, h=0.01 μm, G: α=5°, h=0.1 μm, and H: α=0°, h=0.1 μm.

Preferably, the distance W between the crossings Wo and Wi is 0.03 to 3μm. Preferably, the cap portion has a maximum width Hw of 0.1 to 7 μm asmeasured parallel to the substrate surface. Preferably, the stem portionhas a width Vw adjacent to the substrate surface wherein Vw/Hw is from0.1 to 0.995. At least the substrate surface is preferably formed of ametal or ceramic material.

In a second aspect, the present invention provides a method forpreparing a resist pattern by a patterning process comprising the stepsof coating of a resist composition to form a resist coating, exposure,reversal baking and development in the described order, said resistcomposition comprising a positive resist compound containing a mixtureof an alkali soluble phenol resin and a naphthoquinonediazide and anegative working agent added to the positive resist compound forimparting an image reversal function. According to the invention, amongprocess conditions allowing a resist pattern of inverted trapezoidalcross section to be formed, at least one condition is changed byreducing the thickness of the resist coating, reducing an exposure dose,lowering a reversal baking temperature, reducing a reversal baking time,increasing a developer temperature or extending a developing time suchthat a resist pattern of T-shaped cross section may be formed.

Preferably, upon exposure of the resist coating, light for exposure hasa focal point within the range between -1 μm to +10 μm with respect tothe surface of the resist coating provided that a direction toward thesubstrate is expressed negative and a direction away from the substrateis expressed positive. The reversal baking is preferably effected at atemperature of 100° to 123° C. for 30 seconds to 13 minutes. Typically,the resist pattern has the T-shaped cross section defined in the firstaspect.

In a further aspect of the invention, there are provided amagnetoresistance thin film element comprising a magnetoresistance filmand an electrode film therefor, at least one layer of which is formed bya lift-off technique using a resist pattern of T-shaped cross section asdefined above as a resist cover; a magnetoresistance thin film elementcomprising a magnetoresistance film, an electrode film therefor, and ashield film, at least one layer of which is formed by a millingpatterning technique using a resist pattern of T-shaped cross section asdefined above as a resist cover; and a magnetoresistance thin filmelement comprising a patterned continuous film constituting amagnetoresistance film and an electrode film therefor, said films beingformed by a milling patterning and lift-off technique using a resistpattern of T-shaped cross section as defined above as a resist cover.

According to the present invention, a resist pattern of T-shaped crosssection is produced by utilizing a single layer of resist, that is,entirely homogeneous resist, and controlling patterning conditions asdefined above.

In the resist pattern of T-shaped cross section according to theinvention which is entirely formed of homogeneous resist material on asubstrate, the minimum angle α and the spacing h, both defined above,fall within the range defined and encompassed by tetragon ABCD, whichmeans that the T-shaped cross section has high contrast. When anelectrode pattern or the like for a magnetoresistance thin film elementis formed using this resist pattern, the rejection rate can besignificantly reduced. An acceptance rate of 100% is achievable at best.

Prior to the filing of the basic application (Japanese PatentApplication No. 209950/1995) of the present application, there was knownno example of forming a pattern of T-shaped cross section from a singlelayer of resist through a single step of imagewise exposure. A patternof T-shaped cross section is described in IEEE TRANSACTIONS ONMAGNETICS, Vol. 32, No. 1, January 1996, pages 25-30, published afterthe filing of the basic application. In this article, it is determinedhow the amount of redeposited material left after lift-off is affectedlya change of exposure dose and the temperature of post-exposure baking(corresponding to reversal baking in the present disclosure), with theresults being reported in Table 3. However, the article is silent aboutthe magnitude of exposure dose and baking temperature and the type ofresist used. The resist pattern was formed using broad band light(i-line being cut) as exposure light and reported in Table 3 as having across section overall width (W) of 3.6 μm or more and a T's stem portionheight (H) of 0.2 μm or more. It is noted that the type of exposurelight is judged from the exposure equipment used in the article.

The pertinent article uses a silicon wafer as a substrate and presents aSEM photograph of a cross section of the substrate and the resistpattern as FIG. 4. Insofar as FIG. 4 is concerned, it is believed thatthe resist pattern is formed directly on the surface of a silicon wafer.However, we empirically found it impossible to form a resist pattern ofT-shaped cross section directly on a silicon wafer. A resist pattern islikely to separate from a silicon wafer because a resist as used in thepresent invention is less adhesive to a silicon wafer, a resist patternof T-shaped cross section has a narrow contact area with the substrate,and a fine resist pattern is formed using i-line in a preferredembodiment of the invention. In spite of these problems, the presentinvention enables formation of a fine pattern of T-shaped cross sectionby controlling the patterning conditions as defined above and using asubstrate having a surface other than Si and SiO₂. In contrast, thepertinent article refers nowhere to a fine resist pattern of T-shapedcross section formed using i-line.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the present invention will be apparentwith reference to the following description and drawings, wherein:

FIG. 1 is a schematic cross sectional view of a resist pattern accordingto the invention, showing its T-shaped cross section.

FIG. 2 illustrates steps of a conventional milling process.

FIG. 3 schematically illustrates the step of milling a film through aresist pattern of inverted trapezoidal cross section, showing depositionof milled material on the resist side wall.

FIG. 4 schematically illustrates the step of milling a film through aresist pattern of T-shaped cross section, showing deposition of milledmaterial on the resist side wall.

FIG. 5 illustrates steps of a conventional lift-off process.

FIG. 6 schematically illustrates the deposition of a film of material tobe patterned on a resist pattern of inverted trapezoidal cross sectionin the lift-off process.

FIG. 7 schematically illustrates the deposition of a film of material tobe patterned on a resist pattern of T-shaped cross section in thelift-off process.

FIG. 8 illustrates steps of a combined milling/lift-off process.

FIG. 9 is a graph showing the range of parameters α and h associatedwith the resist pattern of the invention.

FIG. 10 illustrates steps of a process for patterning image reversaltype positive resist.

FIG. 11 illustrates exemplary chemical reactions which take place in theimage reversal positive resist during its patterning.

FIG. 12 shows how the cross-sectional shape of image reversal typepositive resist is affected by each of conditions of each step duringpatterning of the resist provided that the remaining conditions are thesame.

FIG. 13 is a cross-sectional view of the multilayer structure of amagnetoresistance thin film head prepared using the resist pattern ofthe invention.

FIG. 14 is a SEM photomicrograph showing the cross section of a resistpattern designated sample No. 3.

FIG. 15 is a SEM photomicrograph showing the cross section of a fineresist pattern formed on a substrate in Example 2.

FIG. 16 is a SEM photomicrograh showing a continuous film of an MR filmand an MR lead layer formed by a milling and lift-off process using theresist pattern of Example 2.

FIGS. 17 to 20 are SEM photomicrographs showing the cross section of aprior art resist pattern on a substrate.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, a resist pattern is formed on a surface of asubstrate by patterning an image reversal type positive resist by aprocess to be described later. The resist pattern is substantiallyhomogeneous since it is obtained by patterning a single layer of resist.

The image reversal type positive resist is obtained from a resistcomposition comprising a positive resist compound as a base and anegative working agent added thereto for imparting an image reversalfunction. When the resist is patterned by a series of steps: imagewiseexposure →heating (reversal baking)→uniform exposure (floodexposure)→development, an imagewise exposed area is left as in the caseof negative resist.

The resist composition used herein is an image reversal type positiveresist composition comprising a positive resist compound comprising amixture of an alkali soluble phenol resin and a naphthoquinonediazide asa base and a negative working agent added thereto.

The alkali soluble phenol resin used herein includes phenol formaldehydenovolak resins and cresol formaldehyde novolak resins.

The naphthoquinonediazide is a compound having at least onenaphthoquinonediazide group which enhances its solubility in basicsolution upon exposure to actinic radiation. Compounds of variousstructures are known although esters of certain hydroxyl compounds witho-benzoquinonediazide and o-naphthoquinonediazide sulfonic acids arepreferred. Examples include2,2'-dihydroxy-diphenyl-bis-(naphthoquinone-1,2-diazide-5-sulfonic acidester),2,2',4,4'-tetrahydroxydiphenyl-tetra(naphthoquinone-1,2-diazide-5-sulfonicacid ester), and2,3,4-trioxybenzophenone-bis(naphthoquinone-1,2-diazide-5-sulfonic acidester). Especially preferred are esters ofnaphthoquinone-1,2-diazide-5-sulfonic acid with polyhydroryphenylresulting from polycondensation of acetone and pyrogallol as disclosedin Japanese Patent Publication No. 25403/1968.

Examples of the negative working agent include amines, aromatichydrocarbons having a hydroxyl group,1-hydroxyethyl-2-alkylimidazolines, and shellac.

The amines used as the negative working agent include dialkylamines,trialkylamines, secondary or tertiary amines having a hydroxyalkyl group(to be referred to as hydroxyalkylamines, hereinafter), dialkylaminoaromatic hydrocarbons, and cyclic polyamines. Examples of thedialkylamine include diamylamine, diheptylamine and didecylamine;examples of the trialkylamine include tributylamine, triamylamine,trihexylamine and triisoamylamine; examples of the hydroxyalkylamineinclude diethanolamine, N-methylethanolamine, N-methyldiethanolamine,dipropanolamine, and triethanolamine; examples of the dialkylaminoaromatic hydrocarbon include diethylaniline and dipropylaniline; andexamples of the cyclic polyamine include hexamethylenetetramine.

The aromatic hydrocarbon having a hydroxyl group includes aromatichydrocarbons having at least one hydroxyl group capable of forming anester or ether, for example, resins containing a benzene ring having ahydroxyl group and hydroxybenzene compounds. Examples of the resincontaining a benzene ring having a hydroxyl group includephenolformaldehyde novolak resins and cresolformaldehyde novolak resins.Examples of the hydroxybenzene compound include pyrogallol,fluoroglucinol, and 2,2-bis(4-hydroxyphenyl)propane. Exemplary1-hydroxyethyl-2-alkylimidazolines are those having an alkyl group of 7to 17 carbon atoms and mixtures thereof.

Preferred as the negative working agent are triethanolamine,N-methylethanolamine, N-methyldiethanolamine, diethylaniline,hexamethylenetetramine, tributylamine, triisoamylamine,meta-cresolformaldehyde resins, shellac, and1-hydroxyethyl-2-alkylimidazolines.

The amount of the negative working agent used per 100 parts by weight ofthe resist compound is about 0.005 to about 1 part by weight, preferablyabout 0.01 to about 0.3 part by weight of amine; about 0.005 to about 10parts by weight, preferably about 0.01 to about 3 parts by weight ofaromatic hydrocarbon having a hydroxyl group or shellac; or about 0.005to about 0.1 part by weight, preferably about 0.01 to about 0.07 part byweight of 1-hydroxyethyl-2-alkylimidazoline.

in addition to the above-mentioned components, the photosensitive resincomposition used herein may contain various additives. For example,resins capable of uniformly mixing with the above-mentioned componentsmay be added for enhancing image intensity or as a binder. Exemplaryresins are styrene-maleic anhydride copolymers, styrene-acrylic acidcopolymers, and methacrylic acid-methyl methacrylate copolymers.

For the resist composition of this type, reference is made to JP-B32088/1980, British Patent No. 844,039, and U.S. Pat. No. 4,104,070.

Referring to FIG. 1, the cross-sectional shape of the resist patternaccording to the invention is described. The resist pattern generallydesignated at 110 has a mushroom or T-shaped cross section including astem portion 112 extending from a surface 122 of a substrate 120 andsubstantially constituting the vertical bar of T and a cap portion 114extending from the stem portion 112 in opposite directions, opposed tothe substrate surface 122 with a spacing and substantially constitutingthe horizontal bar of T.

In the cross-sectional shape of FIG. 1, a tangent at the lower edge 116of the cap portion 114 opposed to the substrate surface 122 forms anangle with the substrate surface 122. A minimum of this angle isdesignated by α. A line extending from the outermost edge 118 of the capportion 114 perpendicular to the substrate surface 122 intersects withthe substrate surface 122 at a point Wo. The side edge of the stemportion 112 intersects with the substrate surface 122 at a point Wi. Thespacing between the (downward facing) lower edge 116 of the cap portion114 and the substrate surface 122 at an intermediate position betweenthe points Wo and Wi is designated by h. Note that the intermediateposition is located at a distance of W/2 from point Wo wherein W is thedistance between Wo and Wi.

According to the feature of the invention, the minimum angle α and thespacing h fall within a range defined and encompassed by tetragon ABCDas shown in the h-α graph of FIG. 9 wherein

A: α=0°, h=0.01 μm,

B: α=20°, h=0.01 μm,

C: α=20°, h=0.2 μm, and

D: α=0°, h=0.3 μm.

Preferably, α and h fall within a range defined and encompassed bytetragon AXYZ in the h-α graph wherein

A: α=0°, h=0.01 μm,

X: α=5°, h=0.01 μm,

Y: α=5°, h=0.15 μm, and

Z: α=0°, h=0.15 μm.

More preferably, α and h fall within a range defined and encompassed bytetragon AXGH in the h-α graph wherein

A: α=0°, h=0.01 μm,

X: α=5°, h=0.01 μm,

G: α=5°, h=0.1 μm, and

H: α=0°, h=0.1 μm.

In a resist pattern of T-shaped cross section, the setting of α and hwithin the range of tetragon ABCD allows for effective lift-off and ionmilling, ensuring a rejection rate of less than 20%. A resist pattern ofsuch definite T-shaped cross section formed from a single layer ofresist has never been available in the art. It is noted that α=0° meansthat the tangent at the lower edge 116 of the cap portion 114 isparallel to the substrate surface 122.

In FIG. 1, the distance W between points Wo and Wi is preferably 0.03 to3 μm, more preferably 0.1 to 3 μm, most preferably 0.2 to 1 μm. Therejection rate is further reduced by setting W within this range.

Other parameters associated with the resist pattern with T-shaped crosssection according to the invention are described below.

The resist pattern 110 has a height T from the substrate surface 122,which is preferably 0.3 to 3 μm, more preferably 0.4 to 2 μm, mostpreferably 0.4 to 1 μm. With a height T outside the range, it issometimes difficult to define a T-shaped cross section. With a height Tbelow the range, the pattern would be useless as a resist cover. When apattern having a height T beyond the range is used as a resist coverduring milling, the milled pattern is undesirably beveled at its end,approaching parallel to the substrate surface.

Further in FIG. 1, a line extending from point Wi tangent to the sideedge of the stem portion 112 and upward from the substrate forms anangle D with a line extending parallel to the substrate surface 122 andinward of the stem portion 112. The angle β is preferably 10° to 160°,more preferably 70° to 110°.

Furthermore, a line extending from the substrate surface 122 and tangentto the side edge (118) of the cap portion 114 at a height of T/3 fromthe substrate surface 122 forms an angle γ with a line extendingparallel to the substrate surface 122 and away from the stem portion112. The angle γ is preferably 20° to 120°, more preferably 60° to 100°,most preferably 80° to 90°.

Moreover, the cap portion 114 in FIG. 1 has a maximum width Hw which ispreferably 0.1 to 7 μm, more preferably 0.3 to 3 μm as measured parallelto the substrate surface 122.

Additionally, the stem portion has a width Vw adjacent to the substratesurface 122 wherein Vw/Hw is preferably from 0.1 to 0.995, morepreferably 0.15 to 0.95.

It is noted that the resist pattern 110 with T-shaped cross sectiongenerally has a concave top surface. The top surface can be flat orconvex when the width Hw is small.

In the disclosure, the term "substrate surface" is a surface of asubstrate to which the stem portion of the resist pattern is locatedcontiguous. Where a resist pattern is formed on a surface of a film tobe milled, for example, the surface of that film to be milled is thesubstrate surface.

For the substrate surface on which the resist pattern with T-shapedcross section is formed, metal materials and ceramic materials arepreferably used. Preferred examples of the metal material used hereininclude metals such as Cr, Al, W, Te, Mo, Fe, Ni, Co, Mn, Ti, Ta, Au,Ag, and Cu and alloys such as Fe--Ni, Ni--Mn, Fe--Ni--Co, and Fe--Coalloys. Preferred examples of the ceramic material used herein includemetal oxides such as NiO, Al₂ O₃, and ZrO₂, composite metal oxides suchas LiNbO₂, LiTaO₃, and ferrite, and carbides such as AlTiC. Thecrystallinity of these materials is not critical.

On a substrate having a surface of any of the above-mentioned materials,a resist pattern having a characteristic cross-sectional configurationcan be formed. It is noted that the present invention excludes the useof silicon single crystal substrates which are commonly used in themanufacture of semiconductor devices. We empirically found that when theabove-mentioned resist composition was applied to a silicon singlecrystal substrate, a resist pattern having a characteristiccross-sectional configuration could not be formed. The present inventionalso excludes the use of a substrate whose surface is composed ofsilicon oxide, typically SiO₂ because a desired resist pattern can notbe formed as in the case of silicon substrates.

Next, the method for forming a resist pattern of a T-shaped crosssection is described.

FIG. 10 illustrates a process for patterning an image reversal typepositive resist. FIG. 11 illustrates chemical reactions which take placein the resist during the patterning process. Stages of the process forpatterning an image reversal type positive resist are described. Fordetail, reference is made to M. Spac et al., "Mechanism and lithographicevaluation of image reversal in AZ5214 photoresist," Proc. of conferenceon photopolymers principle processing and materials, Ellenville (1985).The following description refers to the use of a basic amine as anegative working agent.

Stage 1: Exposure

In stage 1, an image reversal type positive resist composition 2 iscoated onto an upper surface of a substrate 1 as shown in FIG. 10. Afterprebaking, the resist film on the upper surface is exposed to UVradiation A (wavelength 300 to 500 nm) through a mask 3 having apredetermined pattern. The resist film now includes an exposed area 4and an unexposed area 5. In the exposed resist area 4,diazonaphthoquinone undergoes Wolf rearrangement into indenecarboxylicacid (see Scheme 1 in FIG. 11). The indenecarboxylic acid undergoesacid-alkali reaction with the basic amine used as a negative workingagent into a somewhat unstable amine salt of carboxylic acid (see Scheme2 in FIG. 11).

Stage 2: Reversal Baking

After the reaction of Scheme 2, the resist is heated at 90° to 130° C.for reversal baking (RB). With this heating, the amine salt ofcarboxylic acid quickly converts into an indene insoluble in aqueousbase through carbonyl-removal reaction (see Scheme 3 in FIG. 11). Theindene is not only insoluble in aqueous base, but inert to subsequent UVirradiation and heat. Since this reversal baking step corresponds topost-baking in a conventional process, the instant process eliminates aneed for post-baking.

Stage 3: Flood Exposure

In stage 3, the resist is exposed to UV radiation B. In the unexposedportion 5 of the resist which has been shielded during the firstexposure, diazonaphthoquinone as a photosensitive group converts intoindenecarboxylic acid soluble in aqueous base (see Scheme 1 in FIG. 11).Subsequent reaction with basic amine yields an amine salt of carboxylicacid (see Scheme 2 in FIG. 11). This amine salt of carboxylic acid isalso soluble in aqueous base. Since the UV radiation B does notparticipate in pattern formation, its wavelength is not critical and maybe the same as the wavelength of UV radiation A. Although flood exposureis not always needed, a developer having a relatively high concentrationmust be used and scum can generate during development if flood exposureis omitted.

Stage 4: Development

Finally, the resist is developed with aqueous base whereupon theunexposed area 5 is dissolved away and the exposed area 4 is left.Patterning of the resist film is completed in this way.

Commercially available products of image reversal type positive resistare Resist AZ5200E series from Hoechst. The detail of this resist isdescribed in M. Bolzen, "Submicron processing technology by imagereversal of positive photoresists," Densi-Zairyo (Electronic Material),6, 1 (1986).

Now referring to FIG. 12, it is described how one of conditions in eachstage of the process for patterning an image reversal type positiveresist affects the cross-sectional configuration of resist, providedthat the remaining conditions are the same.

(1) Substrate Surface

The relation of the resist's cross-sectional configuration to patterningconditions does not depend on the type of substrate and whether or notthe substrate surface is treated (as by HMDS gas phase treatment). It ispreferred to omit surface treatment.

(2) Resist Coating Thickness, Pre-baking Temperature and Time

As the thickness of a resist coating is reduced, the portion of aninverted trapezoidal resist shape which is in contact with the substrateis constricted or formed with a slit (into a neck shape) and this slitbecomes wider so that the cross section changes from an invertedtrapezoid to a T shape. Preferably the resist coating has a thickness of3 μm or less after pre-baking. The lower limit of the resist coatingthickness is preferably about 0.3 to 0.5 μm. The pre-baking temperatureand time have little influence on the cross-sectional configuration ofresist. Temperatures below the reversal baking temperature arepreferred.

(3) Exposure Dose

As the dose of exposure is reduced, the portion of an invertedtrapezoidal resist shape which is in contact with the substrate isconstricted or formed with a slit (into a neck shape) and the crosssection changes from an inverted trapezoid to a T shape. Although theoptimum dose varies with the type of optical aligner and the wavelengthdistribution of light to be irradiated (including UV, excimer and otherlaser light, X-ray, and electron beam), a dose of 10 to 500 mJ/cm² ispreferred based on our experimentation. More particularly, the dose ispreferably 100 to 500 mJ/cm², more preferably 100 to 400 mJ/cm² mostpreferably 100 to 330 mJ/cm² when broad band light with i-line(wavelength 365 nm) cut or g-line (wavelength 436 nm) is used. The doseis preferably 10 to 100 mJ/cm², more preferably 30 to 60 mJ/cm² wheni-line (wavelength 365 nm) is used. It is noted that in the manufactureof a magnetoresistance (MR) thin film element, i-line or radiation ofshorter wavelength or electron beams are preferably used as the exposurelight in order to provide an MR film with a fine pattern. None of thefine resist patterns which were heretofore produced through i-lineexposure by prior art techniques had a satisfactory T-shaped crosssection.

Also the height of a slit or constriction formed in that portion of aresist pattern contiguous to the substrate can be adjusted bycontrolling the focal point of exposure light. More particularly, as thefocal point is shifted from the resist coating surface toward thesubstrate (this is expressed with a negative (-) sign), the height of aconstriction or slit is reduced. As the focal point is shifted from theresist coating surface in a direction opposite to the substrate (this isexpressed with a positive. (+) sign), the height of a constriction orslit is increased. Preferably the focal point is located in the range of-1 μm to +10 μm, especially -1 μm to +6 μm with respect to the resistcoating surface. By locating the focal point within this range, thespacing h within the range of the invention is readily accomplished.

(4) Reversal Baking (RB) Temperature and Time

As the RB temperature is lowered, the junction of an invertedtrapezoidal resist to the substrate is constricted or formed with a slit(into a neck shape) and this slit becomes wider so that the crosssection changes from an inverted trapezoid to a T shape. The RBtemperature is preferably 100° to 123° C., especially 100° to 118° C. Asthe RB time is reduced (but longer than a necessary time), the tendencythat the junction of an inverted trapezoidal resist to the substrate isconstricted or formed with a slit (into a neck shape) and the crosssection changes from an inverted trapezoid to a T shape is enhanced. TheRB time is preferably 30 seconds to 13 minutes. Reaction as shown inFIG. 11 would not take place if the RB time is too short.

(5) Flood Exposure Dose

The dose of flood exposure has little influence on the cross-sectionalconfiguration of resist. Typically the dose of flood exposure is 100 to600 mJ/cm².

(6) Development and Rinse Conditions

The developer which is an aqueous alkaline solution has little influenceon the cross-sectional configuration of resist. For example, aqueoussolutions of phosphates and tetramethylammonium hydroxide (TMAH) areuseful. As the developing temperature is higher and/or as the developingtime is longer, the junction of an inverted trapezoidal resist to thesubstrate is constricted or formed with a slit (into a neck shape) andthis slit becomes wider so that the cross section changes from aninverted trapezoid to a T shape. Preferred developing conditions include1 to 3% aqueous solution of sodium phosphate (Na_(n) H₃ -nPO₄), roomtemperature (20°-25° C.), and a time of 30 to 90 seconds. Independent oftemperature and time, the rinse which is deionized water has littleinfluence on the cross-sectional configuration of resist. Preferredrinsing conditions include ultra-deionized water, room temperature(20°-25° C.), and a time of 10 to 180 seconds.

(7) Baking After Development

A baking step may be incorporated for drying after development.Conditions of baking after development have little influence on thecross-sectional configuration of resist.

As mentioned above, in a process for patterning an image reversal typepositive resist, a resist pattern of T-shaped cross section is obtainedwhen conditions of respective steps are properly combined. Moreparticularly, for a particular combination of reversal baking conditionsand developing conditions, for example, a resist pattern of T-shapedcross section is obtained when a resist is exposed in a dose less thanthe minimum dose with which a resist has an inverted trapezoidal crosssection. For a particular combination of exposing conditions anddeveloping conditions, for example, a resist pattern of T-shaped crosssection is obtained when a resist is reversal baked at a temperaturelower than the lowest reversal baking temperature at which a resist hasan inverted trapezoidal cross section. It is thus understood thatcontrol of an exposure dose and reversal baking temperature, especiallycontrol of a reversal baking temperature is effective in forming aresist pattern of T-shaped cross section. A desirable T-shaped crosssection can also be accomplished by controlling other conditions. Theseconditions are shown together in FIG. 12.

Using the resist pattern of the invention described so far, amagnetoresistance thin film element can be manufactured.

FIG. 13 illustrates one exemplary layer structure of a hybrid thin filmmagnetic head comprising a magnetoresistance thin film read head whichis one embodiment of the magnetoresistance thin film element of theinvention and an inductive thin film write head. The magnetoresistancethin film read head 10 includes a substrate 11, an insulating film 12, alower shield layer 13, an insulating film 14, a magnetoresistance (MIR)film 15, an MR lead layer 16 (that is, an electrode film for the MRfilm), and an insulating film 17. The inductive thin film write head 20includes a lower magnetic pole 21, an insulating film 22, an insulatingfilm 23, a coil 24, an upper magnetic pole 25, and a protective layer26. The magnetoresistance thin film read head 10 is combined with theinductive thin film write head 20 to form the hybrid head.

In the hybrid head, the substrate 11 used is generally of ceramicmaterial such as AlTiC. The insulating film 12 is preferably formed ofAl₂ O₃, SiO₂, etc. and has a thickness of about 1 to 20 μm. The lowershield layer 13 is preferably formed of FeAlSi, NiFe, CoFe, CoFeNi, FeN,FeZrN, FeTaN, CoZrNb, CoZrTa, etc. and has a thickness of about 0.1 to 5μm, especially 0.5 to 3 μm. The insulating film 14 is preferably formedof Al₂ O₃, SiO₂, etc. and has a thickness of about 100 to 2,000 Å.

The magnetoresistance film 15 may be a single magnetic layer although itis preferably of a multilayer structure having superposed magneticlayers and nonmagnetic layers. The magnetic layers are preferably formedof NiFe, NiFeRh, FeMn, NiMn, Co, Fe, NiO, NiFeCr, etc. The nonmagneticlayers are preferably formed of Ta, Cu, Ag, etc. The multilayerstructure may be α three-layer structure of NiFeRh/Ta/NiFe or astructure having recurring multilayer units of, for example,NiFe/Cu/NiFe/FeMn, NiFe/Cu/Co/FeMn, Cu/Co/Cu/NiFe, Fe/Cr, Co/Cu orCo/Ag. In the multilayer structure, the magnetic layers preferably havea thickness of about 5 to 500 Å, especially about 10 to 250 Å and thenonmagnetic layers preferably have a thickness of about 5 to 500 Å,especially about 10 to 250 Å. The number of recurring units ispreferably 1 to 30, especially 1 to 20. The magnetoresistance filmpreferably has an overall thickness of about 50 to 1,000 Å, especiallyabout 100 to 600 Å.

The MR lead layer 16 is preferably formed of W, Cu, Au, Ag, Ta, Mo,CoPt, etc. and has a thickness of about 100 to 5,000 Å, especially 500to 3,000 Å. The insulating film 17 is preferably formed of Al₂ O₃, SiO₂,etc. and has a thickness of about 50 to 5,000 Å, especially about 100 to2,000 Å.

Among the constituent layers of the MR thin film head, the insulatingfilms 12, 14, 17, MR film 15, and MR lead layer 16 may be formed byeither the lift-off method or milling patterning method using a resistpattern of the present invention. The lower shield layer 13 ofsubstantial thickness may be formed by the milling patterning methodusing a resist pattern of the present invention. When the MR film 15 andMR lead layer 16 are formed as continuous layers, they may be formed bythe combined lift-off/milling patterning method using a resist patternof the present invention.

Using the resist pattern of the invention, a magnetoresistance thin filmhead can be effectively manufactured in high yields.

EXAMPLE Examples of the present invention are given below by way ofillustration and not by way of limitation.

In the following examples, Resist AZ5214E was used as an image reversaltype positive resist. Resist AZ5214E is a resist composition comprisinga positive resist compound containing a mixture of an alkali solublephenol resin and a naphthoquinonediazide, a basic amine added as anegative working agent, and propylene glycol monomethyl ether acetate asa primary solvent and having a solid content of 28.3%.

Example 1

Resist patterns designated sample Nos. 1 to 8 were formed under theconditions shown in Table 1 while the exposure dose, focal point, and RBtemperature were changed for each sample as shown in Table 2. For eachsample, 1,000 specimen were prepared so as to fall in the range of everyparameter.

                  TABLE 1                                                         ______________________________________                                        Substrate:   AlTiC having an Al.sub.2 O.sub.3 surface layer                   Substrate surface                                                                          none                                                             treatment:                                                                    Resist:      AZ5214E by Hoechst                                               Resist coating thickness:                                                                  ˜1.8 μm as pre-baked                                    Pre-baking temperature/                                                                    95° C., 6 min. (direct hot plate)                         time:                                                                         Aligner:     stepper Ultrastep Model 1500 by Ultratech,                                    NA = 0.28, focus (see Table 2), UV:                                           broad (i-line cut)                                               Exposure dose:                                                                             see Table 2 (mask width: 2.0 μm)                              RB temperature:                                                                            see Table 2 (hot plate)                                          RB time:     5 min.                                                           Flood aligner:                                                                             parallel light aligner model PLA-501F by                                      Canon K.K.                                                       Flood exposure dose:                                                                       500 mJ/cm.sup.2                                                  Developer, temp., time:                                                                    Micro Posit Developer (:H.sub.2 O = 1:1) by                                   Shipley Co., Inc., 23° C., 70 sec. (paddle,                            contacted with a pool of developer for                                        development)                                                     Rinse, temp., time:                                                                        ultra-deionized water, 23° C., 60 sec. (paddle)           Baking after none                                                             development:                                                                  ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    Sample                                                                            Dose Focus RB temp.                                                                            α                                                                            h      Rate of                                      No. (mJ/cm.sup.2)                                                                      (μm)                                                                             (°C.)                                                                        (°)                                                                         (μm)                                                                              rejection**                                  __________________________________________________________________________    1*  100 to 330                                                                         -10 to <-4                                                                          100 to <118                                                                         0 to <5                                                                            0 to <0.01                                                                           ≧40%                                  2   100 to 330                                                                         -4 to <-1                                                                           100 to <118                                                                         0 to <5                                                                            0.01 to <0.03                                                                        20 to <40%                                   3   100 to 330                                                                         -1 to <+6                                                                           100 to <118                                                                         0 to <5                                                                            0.03 to 0.1                                                                          <10%                                         4   100 to 330                                                                         +6 to +10                                                                           100 to <118                                                                         0 to <5                                                                            >0.1 to 0.2                                                                          10 to <20%                                   5*  100 to 330                                                                         >+10  100 to <118                                                                         >2.5 to <5                                                                         >0.3   ≧40%                                  6   330 to 400                                                                         -1 to <+6                                                                           118 to <123                                                                         >5 to 20                                                                           0.03 to 0.1                                                                          10 to <20%                                   7   330 to 400                                                                         +6 to +10                                                                           118 to <123                                                                         >5 to 20                                                                           0.1 to 0.2                                                                           10 to <20%                                   8*  500  -10 to <-4                                                                          130   >20  0 to <0.01                                                                           ≧40%                                  __________________________________________________________________________     *comparison                                                                   **calculated from test results of outer appearance and electromagnetic        properties                                                               

These samples were measured for minimum angle α and spacing h definedpreviously using a field emission electron beam SEM (ULSI high-precisionouter dimension rating equipment S-7000 by Hitachi K.K.). The resultsare also shown in Table 2. Sample No. 3 was measured for W, T, β, γ, Hw,and Vw defined previously, finding W=˜0.75 μm, T=˜1.8 μm, β=˜135°,γ=˜90°, Hw=˜2.4 μm, and Vw/Hw=˜0.3. Other samples were similarlymeasured to find equivalent results.

FIG. 14 is a photomicrograph through the above-mentioned SEM of thecross-sectional configuration of Sample No. 3 resist pattern. It is seenthat a resist pattern of T-shaped cross section with a satisfactorycontrast was obtained. The resist pattern shown in FIG. 14 was formed ona silicon substrate surface coated with an Al₂ O₃ layer which was easyto cut.

These samples were formed on a metal oxide Al₂ O₃. (The substratesurface was Al₂ O₃ although the substrate itself was AlTiC.) Values of αand h equivalent to those shown in Table 2 were obtained when resistpatterns were formed as in Sample No. 3 except that metals such as Ni,Cr, and Ta, alloys such as Fe--Ni and Fe--Ni--Co, and composite metaloxides such as LiNbO₃ were used as the substrate surface. The resultingresist patterns had a T-shaped cross section and a satisfactorycontrast.

The following experiment was carried out in order to examine the millingpatterning performance of the resist pattern samples. On a surface of asubstrate wherein the substrate itself was AlTiC and surface coveredwith an Al₂ O₃ coating, NiFe was uniformly deposited by sputtering to athickness of 0.06 μm. By the lift-off method (conditions are shownbelow), milling patterning method (ion milling conditions are shownbelow), and combined method (conditions are shown below) using theresist patterns of sample Nos. 1 to 8, magnetoresistance thin filmmagnetic heads of the layer structure shown in FIG. 13 were prepared,1,000 heads for each of the samples.

Lift-off Conditions

Organic solvent: acetone

Dipping time: 30 min.

Ion Milling Conditions

Type of ion: Ar⁺

Gas pressure: 1.5×10⁻¹ Torr

Accelerating voltage: 300 V

Accelerating current: 250 mA

Milling angle: 90° (relative to the substrate surface)

Time: 8 min.

Combined Method Conditions

The above-mentioned ion milling conditions and lift-off conditions wereused in combination.

The MR thin film magnetic heads were examined for outer appearance andelectromagnetic properties, from which a rate of rejection wascalculated. The results are also shown in Table 2. It is evident fromTable 2 that using inventive samples having α and h within the specificranges, magnetic heads can be prepared at a very low rate of rejection.

In the manufacture of these magnetic heads, the shield film in the layerstructure of FIG. 13 was formed by the milling patterning method, andthe continuous film of MR film and electrode film therefor formed by thecombined method. Equivalent results were obtained when a MR film wasformed by the milling patterning method and an electrode film thereforwas formed by the lift-off method.

Example 2

A resist pattern sample was prepared under the conditions shown in Table3.

                  TABLE 3                                                         ______________________________________                                        Substrate:   Si having an Al.sub.2 O.sub.3 surface layer                      Substrate surface                                                                          none                                                             treatment:                                                                    Resist:      AZ5206E by Hoechst                                               Resist coating thickness:                                                                  ˜0.7 μm as pre-baked                                    Pre-baking temperature/                                                                    95° C., 6 min. (direct hot plate)                         time:                                                                         Aligner:     stepper FPA-3000i4 by Canon K.K.,                                             NA = 0.45, focus: ±0.00 μm, UV: i-line                     Exposure dose:                                                                             50 mJ/cm.sup.2 (mask width: 0.55 μm)                          RB temperature:                                                                            113° C. (hot plate)                                       RB time:     3 min.                                                           Flood aligner:                                                                             parallel light aligner model PLA-501F by                                      Canon K.K.                                                       Flood exposure dose:                                                                       200 mJ/cm.sup.2                                                  Developer, temp., time:                                                                    Micro Posit Developer (40% aqueous solution)                                  by Shipley Co., 23° C., 50 sec. (paddle,                               contacted with a pool of developer for                                        development)                                                     Rinse, temp., time:                                                                        ultra-deionized water, 23° C., 60 sec. (paddle)           Baking after none                                                             development:                                                                  ______________________________________                                    

A cross section of this sample was similarly examined by means of SEM,finding α=˜0°, h=˜0.02 μm, W=˜0.26 μm, T=˜0.5 μm, β=˜80°, γ=˜70°,Hw=˜0.65 μm, and Vw/Hw=˜0.21.

FIG. 15 is a SEM photomicrograph of a cross section of this sample.

The following experiment was carried out in order to examine thepatterning performance of this resist pattern sample. On an Al₂ O₃coating surface of an AlTiC substrate, a magnetoresistance film of amultilayer structure was formed by sputtering. The MR film had acomposition and thickness of NiFeRh/Ta/NiFe/Ta=130/100/200/50 Å. Theresist pattern sample was formed on the MR film as a resist cover.Patterning was carried out by the milling method. With the resist coverkept unchanged, an electrode film for the MR film (that is, MR leadlayer) having a multilayer structure was formed by the lift-off method,obtaining a continuous film of the MR film and MR lead layer. The MRlead layer had a composition and thickness ofTiW/CoPt/TiW/Ta=100/500/100/1000 Å. An SEM photomicrograph of thiscontinuous film is shown in FIG. 16. In this continuous film, the MRfilm had a width (corresponding to a track width when applied to amagnetic head) of 0.36 μm.

Thousand MR thin film magnetic heads were similarly prepared to examinea rate of rejection as in Example 1. The rate of rejection was 10% orless. It is thus evident that according to the invention, MR thin filmmagnetic heads with a narrow track width can be consistentlymanufactured.

The present invention has the following benefits. (1) By controllingaccording to the invention conditions in a conventional patterningprocess which otherwise produces only an inverted trapezoidal crosssection, a resist pattern of T-shaped cross section with a high contrastis readily formed using a single layer of resist. (2) The width (Hw inFIG. 1) of the T-shaped cross section, the width (Vw) of the stemportion at the joint to the substrate, and the width (W) of theconstriction or slit to the joint to the substrate, and the height (h)of the constriction can be controlled within a certain range in areproducible manner. (3) Owing to the benefit mentioned just above, whenthe resist pattern of T-shaped cross section according to the inventionis used as a mask pattern during lifting-off and dry etching, thecross-sectional shape of the mask pattern can be optimized in accordancewith the thickness and patterning width of a film to be patterned. Theyields of lifting-off and dry etching are increased. (4) A resistpattern of cross section having a width of less than 1 μm can be formed.This enables formation of lift-off and dry etching patterns with a widthof less than 1 μm. (5) A resist pattern of T-shaped cross section can beformed even by exposure with UV radiation. The cost of equipment forexposure can be reduced because of an eliminated need for expensiveequipment such as an excimer laser. (6) A prior art method was verycumbersome in forming a resist pattern of T-shaped cross section since aplurality of steps of exposure and wet development each requiring maskalignment are involved. According to the invention, since each ofexposure and wet development steps can be completed once, the patterningprocess becomes simple, reducing the processing time. (7) Owing tobenefits (5) and (6), lift-off and dry etching patterns can be formed atlow cost.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in the light of theabove teachings. It is therefore to be understood that within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically described.

I claim:
 1. In a method for preparing a resist pattern by a patterningprocess comprising the steps of coating of a resist composition to forma resist coating, exposure, reversal baking and development in thedescribed order, said resist composition comprising a positive resistcompound containing a mixture of an alkali soluble phenol resin and anaphthoquinonediazide and a negative working agent added to the positiveresist compound for imparting an image reversal function, theimprovement whereinamong process conditions allowing a resist pattern ofinverted trapezoidal cross section to be formed, at least one conditionis changed by reducing the thickness of the resist coating, reducing anexposure dose, lowering a reversal baking temperature, reducing areversal baking time, increasing a developer temperature or extending adeveloping time such that a resist pattern of T-shaped cross section maybe formed.
 2. A method for preparing a resist pattern of T-shaped crosssection according to claim 1 wherein upon exposure of the resistcoating, light for exposure has a focal point within the range between-1 μm to +10 μm with respect to the surface of the resist coatingprovided that a direction toward the substrate is expressed negative anda direction away from the substrate is expressed positive.
 3. A methodfor preparing a resist pattern of T-shaped cross section according toclaim 1 wherein the reversal baking is effected at a temperature of 100°to 123° C. for 30 seconds to 13 minutes.
 4. A method for preparing aresist pattern of T-shaped cross section according to claim 1 whereinthe resist pattern has the T-shaped cross section including a stemportion extending from the substrate surface and substantiallyconstituting the vertical bar of T and a cap portion connected to thestem portion, opposed to the substrate surface with a spacing andsubstantially constituting the horizontal bar of T,provided that α is aminimum of the angle which is defined between a tangent at the loweredge of said cap portion opposed to the substrate surface and thesubstrate surface, and h is the spacing between the lower edge of thecap portion and the substrate surface at an intermediate positionbetween the crossing Wo between a line extending from the outermost edgeof the cap portion perpendicular to the substrate surface and thesubstrate surface and the crossing Wi between the side edge of the stemportion and the substrate surface, said minimum angle α and said spacingh fall within a range defined and encompassed by tetragon ABCD in a h-αgraph whereinA: α=0°, h=0.01 μm, B: α=20°, h=0.01 μm, C: α=20°, h=0.2μm, and D: α=0°, h=0.3 μm.